In actuality, it's just a "slide in" (from the side) filter
If that is your only change, the filter really won't change air flow THAT much, and you won't have to adjust your mixture THAT much. After all, what goes in still has to go out.
As far as drilling or removing the door...I still don't understand that one...and I don't mean because of the "intended" benefits of better airflow. I don't know that anyone has ever proven that there is any real improvement from doing that anyway. Do so if you want.
The biggest benefit for the K&N is that it is reusable forever.